<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>

    <video id="video" autoplay="" style='width:640px;height:480px'></video>

    <button id="paizhao">拍照</button>

    <canvas id="canvas" width="640" height="480"></canvas>

    <script type="text/javascript">

        var video = document.getElementById("video");

        var context = canvas.getContext("2d");

        var errocb = function () {
            console.log("sth srong");
        }

        if (navigator.getUserMedia) {
            navigator.getUserMedia({ "video": true }, function (stream) {
                video.src = stream;
                video.play();
            }, errocb);

        } else if (navigator.webkitGetUserMedia) {
            navigator.webkitGetUserMedia({ "video": true }, function (stream) {
                video.src = window.webkitURL.createObjectURL(stream);

                video.play();

            }, errocb);

        }

        document.getElementById("paizhao").addEventListener("click", function () {

            context.drawImage(video, 0, 0, 640, 480);

        });

    </script>

</body>

</html>